Membrane bioreactors (MBR) have been utilized in wastewater treatment processes to reduce contaminants in domestic wastewater using a combination of biological treatment and physical separation by membrane filtration, MBR processes have significant advantages over the conventional activated sludge process (CASP). These advantages have led to increased development of MBR processes for use in various fields, including municipal wastewater treatment, landfill leachate treatment, domestic water reuse, and drinking water reclamation. Despite these advantages, high operating costs have prevented wide-spread use of MBR systems in many applications. The costs of MBR systems have remained high in part due to high costs of filter membranes and high costs of mitigating membrane fouling. Membrane fouling mitigation is associated with up to 70% of MBR operating costs. Because filter membranes carry such a high cost, great importance is placed on mitigating membrane fouling to prevent filter membranes from becoming clogged and no longer useable,
Known mitigation methods, such as air scouring, promote back-transport of particles from membrane surfaces during MBR operation in order to return trapped particles to bulk solution for treatment, thereby reducing membrane fouling rates. This has traditionally been accomplished using aeration devices, such as diffusers, venturis, and other such nozzles that promote the mixing of air and wastewater while increasing fluid velocities within the system. Although, somewhat effective at reducing membrane fouling rates, known methods of fouling mitigation may not be optimum. For example, known methods of membrane fouling mitigation may not effectively promote back-transport at high enough rates for wide-spread applications of MBR processes. Further, known devices and methods may not efficiently mitigate membrane fouling when wastewater is recirculated at high rates within the system.
An exemplary membrane bioreactor system is disclosed by Park et al. (“Park”) in a study published in 2005 titled “Hydrodynamics and microbial physiology affecting performance of a new MBR, membrane-coupled high-performance compact reactor.” Specifically, the Park study discloses a membrane bioreactor comprising a submerged hollow fiber membrane near a bottom portion of a tank. A recirculation pump injects mixed liquor, which is a mixture of wastewater and microorganisms that break down organic pollutants, into a two-phase nozzle fitted with a central air tube. Mixed liquor flowing through the nozzle creates a local pressure drop that draws air into the nozzle. The air and mixed liquor form a liquid jet that passes down the draft tube toward the membrane. The liquid jet produces high turbulence and fine air bubbles in the tank.
Although the system of the Park study may be somewhat effective at mitigating membrane fouling under certain conditions, it may become less effective at high recirculation rates. Particularly, it may not effectively mitigate membrane fouling, despite experiencing increased air suction rates, because the aerated wastewater may not promote back-transport at high recirculation rates, thereby still requiring filter membrane replacement. As a result, operation costs due to filter replacement may not be reduced in applications requiring high recirculation rates.
The disclosed system and process address one or more of the problems discussed above and/or other problems of the prior art.